Project Summary Altered membrane currents are implicated in sudden cardiac death. Ischemic cardiomyopathy (ICM) is responsible for three quarters of these deaths. In preliminary data, we show that (i) PERK, part of the unfolded protein response (UPR), is activated early and persistently in a mouse myocardial infarct (MI) model, (ii) inhibiting PERK after MI reduces sudden death, reduces spontaneous, nonsustained ventricular tachycardia (VT), reduces QTc interval, and reduces action potential duration (APD) without negative consequences to contractile function, (iii) the UPR activation prolongs APD, slows AP upstroke, and alters some but not all ion channels, and (iv) PERK inhibition partially reversed APD prolongation and some ion channel downregulations. Hypothesis: We hypothesize that activation of PERK and other UPR sensors reduce mRNA abundance and protein translation of cardiac ion channels. This contributes to current alterations, APD prolongation, and increased arrhythmic risk in ICM. Inhibition of PERK or other UPR effectors can prevent some of the remodeling. In vivo, PERK inhibition will be antiarrhythmic in ICM, in part, by improving conduction velocity and reducing APD. Specific aims: Aim 1: Determine the extent to which PERK inhibition can prevent APD prolongation, electrical remodeling and arrhythmic risk associated with ICM. In this aim, ICM will be induced in mice. APD, electrical remodeling and arrhythmic risk will be compared between mice with and without pharmacological inhibition of PERK starting immediate after infarct or at 3 weeks to test prevention versus treatment strategies. Results will be compared to genetic inhibition of PERK (cardiac specific PERK-knockout (KO)) and to findings in human ICM. Aim 2: Determine the extent to which PERK can contribute to APD prolongation and the alterations of ion channels. Using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with activated UPR, we will determine which other ion channels are altered by UPR and PERK activation and are responsible for APD prolongation. Aim 3: Investigate whether the IRE1 and ATF6? branches of the UPR contribute to APD prolongation and the alterations of ion channels. Using hiPSC-CMs and activating the IRE1 and ATF6? branches of UPR, we will determine whether activation of these two branches contributes to AP changes and downregulation of cardiac ion channels.